Gasket material for pressure vessels and chemical piping requires an array of special properties which is difficult to obtain in any single material. The requirements include conformability with limited cold flow, properties which are essentially antithetical to each other, as well as chemical inertness, operability at high termperature and low cost. Polytetrafluoroethylene (TFE) has been widely used because of the wide range of chemicals to which it is inert. However, it suffers from excessive cold flow, so that in gasket form it cannot be used to withstand internal pressures in excess of 200 psi at 250.degree. F. and in excess of 30 psi at 450.degree. F. This imposes a severe limitation on the practical utility of the material, since there are many applications in which the pressures normally exceed this limit. Moreover, it cannot be used where there is a possibility of a brief surge of pressure above this limit, since the cold flow is relatively rapid.
Other organic fibers which may be used as gasket materials are aramid, manufactured by DuPont under the trade name of "Kevlar", nylon, polyethylene and polypropylene. While these materials exhibit lower cold flow than does TFE, they are not so inert chemically. Accordingly, it would be desirable to provide a gasket material which is operable at higher pressures than is TFE tape, which is lower in cost and which is yet resistant to a wide range of chemicals. The present invention is designed to meet this end.